1. Field of the Invention
This invention relates to the in situ generation and incorporation of polyurethane prepolymers generated within a matrix of bituminous material such as asphalt. The resulting bituminous polyurethane interpenetrating elastomeric network compositions can be applied as coatings and sealants for roofing, coverings, and construction waterproofing applications, as well as other applications.
2. Description of Related Art
Polyurethanes are extensively used as coatings and sealants in housing, construction, furniture, and other industries. Polyurethane prepolymers are generally developed by reacting different polyols with di- or poly- isocyanates in varying ratios. FIG. 2 depicts a reaction between a polyol and diisocyanate. Polyurethanes are hard, water-resistant, slippery when wet, and tend to degenerate when exposed to ultra-violet light.
xe2x80x9cBituminous materialxe2x80x9d is meant to include bitumen, asphalt, coal tar, and performance-rated asphalt. Due to the low cost of bituminous material, its relatively high penetration value when applied to most porous surfaces, weather-resistant nature, and impermeability to water, bituminous material has traditionally been used as a main component of protective films, adhesive binders in asphalt emulsions (M. Lalanne and J. Serfass, U.S. Pat. No. 4,724,245), in blends used for paving and roofing, joint sealants, paints, and other end uses. Existing unreinforced bituminous materials tend to crack during normal seasonal thermal expansion. In addition, typical bituminous materials are difficult to apply and take a long time (days) to cure completely.
Attempts to provide a blend of a liquid, preferably an ambient-curable prepolymer, with bituminous material have been made (H. Lucke, U.S. Pat. No. 4,871,792). In the past, several methods were developed to increase the compatibility between the bituminous binder and polyurethanes, either by using a modified clay (R. J. Janoski, U.S. Pat. Nos. 5,421,876 and 5,319,008), or pre-treating the bituminous materials before mixing with polyurethane prepolymer (M. Shihadeh, U.S. Pat. No. 3,980,597).
Several attempts to develop a rubberized bituminous material using crumb rubber have also been made. Methods are available, reported, and in practice today. Crumb rubber from recycled car and truck tires improves wear resistance (D. W. Causyn and K. Thys, PCT Int. Appl. WO 9221820), lowers temperature fracture properties (G. R. Morrison and S. A. M. Hesp., J. Mater. Sci. 30(10), 2584 (1995) and A. Coomaraswamy, S. Manolis and S. Hesp., Am. Chem. Soc. Div. Fuel. Chem., 41(4), 1322 (1996)); and enhances coating performance and safety of the coated surface (M. Wm. Rouse, Rubber World, 212(2), 23 (1995)). Most of these applications are used in the paving industry, anti-skid mats for playgrounds, and running tracks (H. L. Draper, D. F. Levy, and D. W. Gagle, U.S. Pat. No. 3,547,674).
Apart from the use of crumb rubber, other polymers are used to modify asphalt (M. E. Labib, G. M. Memon, and B. H. Chollar, Prepr. Pap.xe2x80x94Am. Chem. Soc., Div. Fuel. Chem., 41(4), 1209 (1996), I. K. Negulescu and W. H. Daly, Annu. Tech. Conf., Soc. Plat. Eng. 54th (vol. 1), 1175 (1996). The thermoplastic nature of these existing polymer modified bituminous materials limits their coating and sealant applications.
These past attempts to incorporate a resin within a bituminous material have failed for a combination of reasons. First, polyurethanes and bituminous materials are not miscible because polyurethanes are polar, while bituminous materials are non-polar. Second, without more, the reaction rate between the reagents forming the polyurethane (polyol and isocyanate) is slow enough that the reagents separate from the bituminous material, polymerize, and form non-integrated, heterogeneous products. These heterogeneous products do not produce synergistic qualities such as increased strength and ease of application.
Owing to the advantages of polymer modified bituminous materials, this invention is a further novel modification of bituminous materials with polyurethanes, by in situ generation of their prepolymers, so that the prepared bituminous polyurethane interpenetrating elastomeric network compositions will be stronger, easier to apply, and less expensive than the conventional mixing of polyurethane prepolymers with bituminous material. The mixing of polyurethane prepolymer with the rubberized bituminous material at the molecular level results from improved miscibility. In turn, improved miscibility improves the physical and mechanical properties of the coatings and sealants. Suitable bituminous materials include, but are not limited to, asphalt, coal tar, polymer modified asphalt, oxidized, and unoxidized asphalt.
According to the method of the invention, the polyol and bituminous materials are mixed separately from the isocyanate. The polyol and molten bituminous material are more miscible than prepolymerized polyurethane and bituminous material. Next, a catalyst and curing agent can be added to either of the polyol or isocyanate. The polyol/bituminous material mixture is then mixed thoroughly with the isocyanate immediately before application. The catalyst causes the polyurethane to form rapidly (in as little as seconds) within the bituminous material to form an effectively-homogenous, three-dimensional matrix.
The properties of the resulting matrix can be controlled by changing the formulation. By increasing the proportion of cross-linking agents such as diisocyanate, the strength of the product is increased. By reducing the proportions of cross-linking agents, the flexibility of the materials can be increased. Increased strength is useful in applications such as building reinforcement. Increased flexibility is useful in applications such as coating a running track or manufacturing o-rings.
A curing agent can be added to decrease the time before a permanent matrix is formed. Curing agent can reduce the gelation time to as little as seconds. Reduced gelation time is useful to expedite the completion of jobs such as filling cracks and crevices. A curing agent can be omitted or limited in situations requiring a longer time before setting. A longer setting time can be desirable when the material is used as an adhesive and time is required to position the materials being adhered.
These materials were tested as coatings, sealants, and adhesives on a range of substrates. These materials can be generated at the job site, and are applied to various surfaces, through our uniquely designed pumping, metering, mixing, and spraying system.
The present invention achieves the additional advantages set forth below by providing a unique method of modifying polyurethanes into useful compositions which meet the essential requirements for coatings and sealants. The asphalt/bitumen components provide processability of the resultant coatings and sealants. The rubber component provides frictional and abrasion resistance as well as ultra-violet radiation resistance to the coatings and sealants. The unique method of producing these polymers yields easy applications as well as an overall decrease in the coating cost.
The bituminous polyurethane interpenetrating elastomeric network compositions produced have improved adhesion. The highly reactive urethane prepolymer gives better adhesion to different substrates. The coated substrates were evaluated for their physical and mechanical properties, adhesion, static and dynamic puncture resistance, wind-up lift test, and other properties. Bituminous polyurethane interpenetrating network elastomer compositions of the invention are resistance to solvents, oil, and acid.
The reaction kinetics were followed by measuring the torque increase as a function of reaction time. The gelation time is measured at the maximum torque. For testing, the bituminous polyurethane interpenetrating network elastomeric compositions were hot-sprayed-applied (200xc2x0 F. -350xc2x0 F.) on different substrates such as concrete, metal, wood, built-up roofing systems, polyurethane foams, and other construction materials with a specially designed spray applicator system. The present invention composition is preferably formed, through a melt polymerization process, such as an in situ melt polymerization reaction. The composition is preferably solventless and fillerless.
Therefore, an object of the present invention is to provide a composition which is superior in providing coating and sealing over a substrate.
Another object of this invention is to provide a method of preparing such a composition at or near the site of application, easily and economically.
Another object of this invention is to provide a sealing and coating composition which provides superior traction performance.
In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawing.